Another P.I. link

hello all ,
 i still have a zilog z80 chip somewhere , still have a 48k rubber key model , and the peice de resistance,,,,
a 128k +3 with a 178k disc drive ,,,,,,whhhhooooh ! keep for poss robot making , maybe .

xavier had a real good look at the pcb , the 2 lm741's  next to each other , i see neg rail going to pin 4 on each of them ,
but + looks to be going to pin 8 , pin 7 is + on a 741 ,

on u5 pin 7(+) and 6(out) are joining,
 hang on a moment , i know whats happened , one of the pics that 6666
 posted still has the pin numbers from the old dual op-amp device on it.

now i feel guilty , i should have spent the time drawing up my version of the schematic in the first place ,and posting it regardless of my drawing quality , my fault , sorry.

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		Quote:			Posted by homefire
	Last time I did any Programing was on a ZX-81

Somebody call a doctor. I just had a serious flashback!

I feel . . . so wounded.

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I cut my computer teeth on the Z80 and actually had a ZX-81 for which I designed and sold two memory add ons. One of 16kb and the other for 64kb. The beast couldn't address any more than that unfortunately. I must have sold 10,000 of them before the well ran dry and cheap machines started becoming popular.

I love the PIC chips. There are some low cost entry level systems out there. You should look into it.

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Sorry xavier I updated the 741 pin numbers on the cct a few posts back
here is the latest with threshold update
cheers



Posted on: August 15, 2011, 07:51:44 PM

---

Dooley with this inductance thing, over on GT , I have mentioned my problem with the inductance of the original HH coil, 26 turns, 10inch, .4mm enamel copper wire

Using the Qiaozhi calculator (Version 2.0 ) which is based on enamel copper wire
the value I am reading on my meter is getting closer to the calc, 577uH, the tighter I wrap it.
its taken me some time to check this.
try making a coil with just enamel copper wire, tightly wrap it,  use Q's calculator and see if its close, on your meter,
I think you mentioned your wire is pvc covered
cheers

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hello 6666 ,

yes i used pvc covered wire as apparantly it would be a "faster" coil if the conductors were sepperated ,
poss this has increaced the inductance.

i used Qiaozhi's calculator aswell.

hello xavier ,

all ok now with the 741's , but...........sorry to be a pain , cant see a track / link going from the 1k and back to back diodes to pin (2) - input of the TL071 ,
other thing is , track length / width from the stabillized / heavly capped power supply to the mosfet , quite long and quite thin , poss not strong enough to handle the current , pref mosfet closer to + and - of the big caps with wider tracks , also the supply at the moment is running parrallel for quite a length with the preset pots for th 4538 , may pick up some interferance ,

today going to take a picture of my amatuer'ish stripboard build where volt reg and mosfet on heatsinks are at the sides for cooling , 5xcaps down the middle with thick tracks so everything can have a minimum interferance supply.
also i placed all related components close together , presets right next to dual timer , tried my best to keep track length short on all pulsing circuits.

should get some pics posted soon , today , for all to chuckle at.

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